Rotary tool and its cutting part

ABSTRACT

A rotary tool (T) has a rotary segment ( 10 ) with an opposed surface opposed to a work surface and a plurality of cutting parts ( 20 ) arranged on the opposed surface. Some cutting parts ( 20 ) include tips ( 22   a ) made of a grinding tool segment obtained by binding abrasive grains by a metal binder and the other cutting parts ( 20 ) include tips ( 24   a ) made of a sintered material harder than the grinding tool segment, and the respective cutting parts ( 20 ) are arranged such that the tips ( 24   a ) are located at positions more outward than the tips ( 22   a ) with respect to radial directions of the rotary segment.

TECHNICAL FIELD

The present invention relates to a rotary tool and a cutting partthereof for working outer surfaces of walls and floors of buildings,ships, bridges and the like to remove paints, adhesives and the likeadhered to the outer surfaces.

BACKGROUND ART

A rotary grinder in which a plurality of grinding tool segments arearranged at the outer periphery of a saucer-shaped rotary segment isknown as a tool for working surfaces such as floor surfaces and wallsurfaces of various structures. The respective grinding tool segmentsused to form this grinder are obtained by sintering, for example, amixture of a certain amount of diamond abrasive grains and a metalbinder. A work surface can be abraded by bringing the respectivegrinding tool segments provided on the grinder into contact with thework surface while rotating the entire grinder at high speed.

However, in the case of using the above grinder to remove old filmsadhered, for example, to floor surfaces and wall surfaces (particularlyrubber-made elastic paints and adhesives) in a repair and renovationwork or the like for a concrete structure, the films and the like may bethermally fused and melt by friction heat created between the films andthe respective grinding tool segments to consequently cause adhesion tothe grinding tool segments, with the result that a satisfactory removingwork may not be able to be performed. Further, there is a problem ofbeing difficult to produce a longer tool life because the abrasion speedof the grinding tool segments is relatively high.

Japanese Unexamined Patent Publication No. 7-185923 discloses a rotarytool in which a plurality of cutting devices made of sintered diamondare peripherally fixed at even intervals on a cutting-device mountingsurface defined at the outer periphery of a saucer-shaped rotarysegment. According to this tool, a work surface can be smoothly removedwithout the adhesion by pressing the respective cutting devices againstthe work surface while the rotary segment is mounted on a drive shaft ofa motor and rotated at high speed.

However, the tool disclosed in the above publication has a problem thattips made of the sintered diamond deeply cut into the work surface sincethe tips have good cutting quality. Such excessive cutting-in of thetips leaves cutting marks even in the substrate of the work surface andshortens the tip life due to a damage or breakage by giving anunnecessary load to the tips.

Accordingly, an object of the present invention is to enable asatisfactory removing work by preventing an occurrence of heat adhesionwhile avoiding excessive cutting-in of tips.

DISCLOSURE OF THE INVENTION

In order to solve the above object, the present invention adopts thefollow construction.

Specifically, the present invention is directed to a cutting part of arotary tool provided on an opposed surface of a rotary segment of therotary tool opposed to a work surface and having a tip for scratchingoff a surface portion of the work surface when the rotary segment ispressed against the work surface while being drivingly rotated about anaxis extending in a direction normal to the opposed surface, wherein aninner part of the tool segment with respect to a radial direction ismade of a grinding tool segment obtained by binding abrasive grains by ametal binder and an outer part of the tip with respect to the radialdirection is made of a sintered material harder than the grinding toolsegment (claim 1).

In this cutting part, the radially outer part of the tip, i.e. a partthereof performing more cutting work due to its higher peripheral speed,is made of the hard sintered material having a sharp cutting quality.Thus, the surface portion of the work surface can be lightly removed athigh speed by this part, thereby preventing an occurrence of heatadhesion. On the other hand, the radially inner part of the tip, i.e. apart thereof performing less cutting work due to its lower peripheralspeed, is made of the grinding tool segment (grinding tool segmentobtained by binding the abrasive grains by the metal binder) having arelatively dull cutting quality due to its lower hardness than thesintered material. This can prevent the entire tip from cutting inexcessively deep.

Further, by making the radially outer part of the tip performing morecutting work of the sintered material while making the radially innerpart thereof performing less cutting work of the grinding tool segment,the wear speed of the tip can be made uniform over the entire radialdirection. Thus, unlike the prior technology cutting part whose toolsegment is entirely made of the same material, wear of the radiallyouter part of the tool segment prior to the radially inner part thereofcan be prevented from occurring. As a result, the entire tool life canbe extended.

Further, surface residues of the covering materials which could not beremoved by the tip part made of the hard sintered material can besupplementarily ground off by the grinding edges made of the grindingtool segment. Furthermore, even if the removal by the tip part made ofthe sintered material leaves scratches on the work surface, suchscratches can be ground-off or finished by the grinding edges made ofthe grinding tool segment.

For example, cemented carbide, ceramic, cermet and the like may be usedas the hard sintered material. However, a polycrystalline diamondsintered material (PCD) and a polycrystalline cubic boron nitridesintered material (PCBN) are particularly preferable (claim 2). By usingsuch a particularly hard sintered material, adhesion can be moresecurely prevented from occurring and a longer tool life can be given.

Further, Diamond abrasive grains and CBN abrasive grains are preferablyused as the abrasive grains to be bound by the metal binder.

Japanese Unexamined Utility Model Publication No. 3-7470 discloses acutter bit in which metal-bonded diamond grinding tool segments andcemented carbides are alternately arranged in order to cut reinforcedconcrete. Since the grinding tool segments and the cemented carbides arearranged in peripheral direction (not in radial directions), an effectof preventing an occurrence of adhesion while preventing excessivecutting-in of the tip as in the present invention cannot be obtained.

According to the present invention, not only the radially inner part ofthe tip, but also the entire tip excluding the tip part made of thesintered material are more preferably made of a grinding tool segmentobtained by binding abrasive grains by a metal binder (claim 3). Withsuch a tip, the aforementioned effects can be obtained while theconstruction of the entire cutting part is simplified.

According to the present invention, a ratio of the length of the tippart (radially outer part) made of the hard sintered material to that ofthe remaining part (radially inner part) may be suitably selected basedon the materials and rotating speeds of the respective parts. Generally,the length of the tip made of the sintered material is preferably setwithin a range of 1% to 67% of the entire length of the tip in order toenjoy both the adhesion preventing effect and the excessive cutting-inpreventing effect (claim 4).

The present invention is also directed to a rotary tool, comprising: arotary tool segment having an opposed surface opposed to a work surface,and a plurality of cutting parts arranged on the opposed surface andeach having a tip for scratching off a surface portion of the worksurface in a peripheral direction, the rotary tool scratching off thesurface portion of the work surface by pressing the respective cuttingparts against the work surface while the rotary tool segment isdrivingly rotated about an axis extending in a direction normal to theopposed surface, wherein a grinding tool segment obtained by bindingabrasive grains by a metal binder is arranged on the opposed surface;the cutting parts include tips made of a sintered material harder thanthe grinding tool segment; and the tips made of the sintered materialare provided at positions more outward than the grinding tool segmentwith respect to radial directions of the rotary tool (claim 5).

With this rotary tool, while the tips made of the hard sintered materialand having a sharp cutting quality lightly remove the surface coveringsof the work surface at high speed to prevent an occurrence of heatadhesion, the presence of the grinding tool segment having a lowerhardness than the sintered material and a relatively dull cuttingquality at the position radially inward of these tips suppresses deepcutting-in of the entire tip. Further, the removing work by the tipsmade of the hard sintered material is assisted by the grinding toolsegment. If the work surface is scratched by the removing work by thetips made of the sintered material, such scratches can be ground off orfinished by the grinding tool segment.

As a specific embodiment of this rotary tool, some cutting parts includetips made of the grinding tool segment and the other cutting partsinclude tips made of the sintered material harder than the grinding toolsegment, and the respective cutting parts are arranged such that thetips made of the sintered material are located at positions more outwardthan the tips made of the grinding tool segment with respect to theradial directions of the rotary segment (claim 6). As another specificembodiment, the grinding tool segment has such a shape continuous alonga peripheral direction of the rotary segment, and the cutting partshaving the tips made of the sintered material are provided at positionsmore outward than the grinding tool segment with respect to the radialdirections of the rotary segment (claim 7).

The present invention is further directed to a rotary tool, comprising arotary segment having an opposed surface opposed to a work surface, anda plurality of cutting parts arranged on the opposed surface and eachhaving a tip for scratching off a surface portion of the work surface ina peripheral direction, the rotary tool scratching off the surfaceportion of the work surface by pressing the respective cutting partsagainst the work surface while the rotary segment is drivingly rotatedabout an axis extending in a direction normal to the opposed surface,wherein at least a part of the cutting parts are cutting parts accordingto any one of claims 1 to 4 (claim 8).

With this rotary tool, while the tips made of the hard sintered materialand having a sharp cutting quality lightly remove the surface portion ofthe work surface at high speed to prevent an occurrence of heatadhesion, the presence of the tips made of the grinding tool segmenthaving a lower hardness than the sintered material and a relatively dullcutting quality suppresses deep cutting-in of the tips. Further, theremoving work by the tips made of the hard sintered material is assistedby the tips made of the grinding tool segment. If the work surface isscratched by the removing work by the tips made of the sinteredmaterial, such scratches can be ground off or finished by the tips madeof the grinding tool segment.

In the rotary tool according to claim 8, all the cutting parts of therotary tool may not be necessarily cutting parts according to any one ofclaims 1 to 4. However, if all the cutting parts are cutting partsaccording to any one of claims 1 to 4 and peripherally arranged at evenintervals (claim 9), a smoother removing work can be realized by makingthe cutting ability peripherally uniform.

Further, if the rotary tool comprises at least first cutting partshaving tips made of the sintered material and second cutting partshaving tips made of the grinding tool segment, and the second cuttingparts are arranged such that the tips thereof are located at positionsmore inward than the tips of the first cutting parts made of thesintered material with respect to the radial directions of the rotarysegment (claim 10), both the backing preventing effect and the excessivecutting-in preventing effect can be enjoyed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rotary tool according to a firstembodiment of the present invention when viewed from bottom;

FIG. 2 is a perspective view of the rotary tool when viewed from above;

FIG. 3 is a side view of the rotary tool;

FIG. 4 is a perspective view showing an exemplary driving device onwhich the rotary tool is mounted;

FIG. 5 is a perspective view of the rotary tool of the embodiment of thepresent invention constructed to work painted floors when viewed frombottom;

FIG. 6 is a perspective view of a rotary tool according to a secondembodiment of the present invention when viewed from bottom;

FIG. 7 is a bottom view of the rotary tool of FIG. 6;

FIG. 8 is a perspective view of a rotary tool according to a thirdembodiment of the present invention when viewed from bottom;

FIG. 9 is a bottom view of the rotary tool of FIG. 8;

FIG. 10 is a bottom view of a rotary tool according to a fourthembodiment of the present invention; and

FIGS. 11A and 11B are a bottom view and a front view in section of arotary tool according to a fifth embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention is described with referenceto the accompanying drawings. Although a case where a film applied tothe outer surface of a work surface S is to be removed is illustrated inthis embodiment, working according to the present invention is notlimited thereto. The present invention is also widely applicable toremoval of other “films” such as adhesives, resin sheets and resin tilesadhered to work surfaces or work surfaces made of other materials.

A rotary tool T shown in FIGS. 1 to 4 is comprised of a rotary segment10 made of a metallic plate and a plurality of cutting parts 20 mountedon the rotary segment 10.

The rotary segment 10 integrally includes an outer peripheral portion 11in the form of a flat plate 11 and an inner portion 12 formed inside theouter peripheral portion 11.

The inner portion 12 bulges out upward substantially in the form of acone from the inner edge of the outer peripheral portion 11, and a flatportion 14 parallel with the outer peripheral portion 11 is formed in amiddle part of the inner portion 12. A driving-shaft insertion hole 18is formed in the center of the flat portion 14, and a driving shaft ofan unillustrated driving source is mounted into the insertion hole 18 todrive the entire rotary tool about a center axis O (see FIG. 2) togetherwith the driving shaft. A plurality of through holes 17 are peripherallyformed at an outward-bulging portion (i.e. a portion between the centeraxis O and the outer peripheral portion 11) radially outward of the flatportion 14.

The bottom surface of the outer peripheral portion 11 is a surface(hereinafter, merely “opposed surface”) opposed to the work surface Sshown in FIG. 3 in parallel therewith, and a plurality of cutting parts20 are peripherally arranged on this opposed surface. In the shownexample, eight cutting parts 20 are peripherally arranged at evenintervals, and secured to the opposed surface by means of brazing andscrewing.

Each cutting part 20 includes a cutting-part main body 22 and a hardsintered material partially secured to the cutting-part main body 22 viaa cemented carbide 23.

Each cutting-part main body 22 is in the form of a block obtained bycombining abrasive grains (e.g. diamond abrasive grains or CBN abrasivegrains) by a metal binder (e.g. iron, cobalt, tungsten, or the like). Inthe shown example, each cutting-part main body 22 has an outerperipheral surface substantially arcuate in bottom view and extendingalong the outer periphery of the outer peripheral portion 11, an innerperipheral surface substantially arcuate in bottom view and extendingalong the inner periphery of the outer peripheral portion 11, andopposite side surfaces straight in bottom view and extending in radialdirections of the tool T, and has uniform thickness in its entirety. Ineach cutting-part main body 22, a part located at a downstream side withrespect to rotating direction and at an outer side with respect toradial direction locally is cut off, and the cemented carbide 23 and thehard sintered material 24 shaped to complement for a cut-off part aresecured to this cut-off part.

It is sufficient to make the hard sintered material 24 of a sinteredmaterial harder than the cutting-part main body 22. For example,cemented carbide, ceramic, cermet or the like may be used. Particularlypreferably used are a polycrystalline diamond sintered material havingexcellent hardness and a polycrystalline cubic boron nitride sinteredmaterial having hardness next to the former material. A preferablemethod for forming such hard sintered materials 24 and securing them tothe cutting-part main bodies 22 is, for example, such that diamondpowder as a raw material of the hard sintered material 24 is placed onthe outer surface of a substrate made by the cemented carbide 23 andpressurized, whereby the entirety is integrally sintered to produce atool material made of diamond sintered material, and this tool materialis cut to a shape corresponding to the cut-off part and a surface of thecut tool material at the side of the cemented carbide 23 is secured tothe cutting-part main body 22 by brazing.

With the hard sintered material 24 secured to the cutting-part main body22, a bottom edge 24 a of the hard sintered material 24 at a downstreamside with respect to radial direction and a bottom edge 22 a of thecutting-part main body 22 at a downstream side with respect to radialdirection are aligned in a straight line. The bottom edge 24 a of thehard sintered material 24 forms an outer part of a tip with respect toradial direction, whereas the bottom edge 22 a of the cutting-part mainbody 22 forms an inner part of the tip with respect to radial direction.

Although a tip angle is 90° and a rake angle is 0° in the shown example,these angles may be suitably set according to the specific material andapplication of the cutting-part.

A ratio of entire tip length Lo to length Ls of the bottom edge 24 a asshown in FIG. 1 depends on the material of the hard sintered material24. This ratio is preferably 1% to 67% if the hard sintered material 24is made of a polycrystalline diamond material or polycrystalline cubicboron nitride sintered material. There is a high chance of adhesion ifthis ratio is below 1%, whereas problems caused by excessive cutting-inare likely to occur if this ratio exceeds 67%.

Although the thickness of the hard sintered material 24 may be smallerthan that of the cutting-part main body 22, the lift of the cutting part20 can be maximally extended by equally setting the two thicknesses.

Next, the use and functions of this tool T are described.

1) Mounting onto a Driving Device

First, the tool T is mounted onto a driving device. A portable drivingdevice 30 is shown in FIG. 4 as an example. This driving device 30includes a grip 32 and a tool cover 36 provided at the leading end ofthe grip 32, an unillustrated drive shaft projects in the tool cover 36and a motor or the like for rotating this drive shaft at high speed isbuilt in a driving device main body. Further, the tool cover 36 isconnected with an unillustrated exhaust pump via an air pipe 34.

The rotary segment 10 is connected and fixed at the leading end of thedrive shaft, for example, by inserting the drive shaft of this drivingdevice 30 through the insertion hole 18 formed in the tool T andmounting a nut on an externally threaded portion formed at the leadingend of the drive shaft. In this way, the entire tool T is mounted in thetool cover 36 shown in FIG. 4 and has its rear side (side opposite fromthe work surface S) covered by the tool cover 36.

2) Working by the Tool T

The grip 32 of the driving device 30 is gripped while the drive shaftand the tool T are integrally rotated at high speed and air is exhaustedinside the tool cover 36 via an unillustrated exhaust pipe, and therespective cutting parts 20 are pressed against the work surface (e.g.wall surface) S and moved along the work surface S. In this way, thecoverings on the work surface S is scratched off by the tips of therespective cutting parts 20 rotating at high speed.

Here, since the outer part of the tip with respect to radial direction,i.e. part performing more cutting work due to higher peripheral speed isformed by the hard sintered material 24 having a sharp cutting quality,the coverings on the work surface S can be lightly removed by this part,whereby adhesion of the coverings due to thermal fusion can beprevented. On the other hand, an occurrence that the entire tips deeplycut in can be suppressed since the inner parts of the tips with respectto radial directions, i.e. parts performing less cutting work due totheir low rotating direction are made of metal bound grinding toolsegment (grinding tool segment forming the cutting-part main parts 22)having a relatively dull cutting quality due to its smaller cuttingedges than the sintered material.

Whereas the radially outer parts of the tips performing more cuttingwork are formed by the hard sintered materials 24, the radially innerparts of the tips performing relatively less cutting work are formed bythe above grinding tool segment (the one forming the cutting-part mainbodies 22), whereby the wear speed of the tips can be made uniform overthe entire radial direction. Unlike the prior art cutting parts in whichthe entire tips are made of the same material, the radially outer partsof the tips can be prevented from abrasion prior to the radially innerparts thereof. As a result, the entire tool life can be extended longer.

Further, the removing work by the tips formed by the bottom edges 24 aof the hard sintered materials 24 (hereinafter, “hard sintered materialtips 24 a”) can be assisted by the tips formed by the cutting-part mainbodies 22 made of grinding tool segment (grinding tool segment tips 22a). For example, in the case of using this tool to remove a covering,the coverings which cannot be scratched off by the hard sinteredmaterial tips 24 a can be supplementarily scratched off by the grindingtool edges 22 a. Further, in the case of making a scratch upon theremoving work by means of the hard sintered material tips 24 a, aneffect of grinding off or finishing such a scratch can be expected bythe grinding tool edges 22 a.

Cutting dust produced by such scratching is sucked to the side of thetool cover 36 (side opposite from the work surface S) via the respectivethrough holes 17.

Although the tool T used by being mounted on the portable driving device30 is shown in FIGS. 1 to 4, the present invention is not limitedthereto. For example, in the case of working a so-called “paintedfloor”, the film can be efficiently removed in a comfortable posture bymounting the tool T on a hand-push type processing device or ridableprocessing device which can run on the floor. One example of the tool Tfor such an application is shown in FIG. 5. In a rotary tool T shown, arotary segment 10 is formed into a simple disk shape, and a plurality ofcutting parts 20 are arranged at an outer peripheral portion thereof.Although a cutting-part main body 22 is formed to be triangular inbottom view in the shown cutting part 20, it is quite similar to the oneshown in FIGS. 1 to 4 in that a sintered material 24 is locally providedat a radially outer part.

The work surfaces to be processed according to the present invention arenot limited to the walls and floors of buildings. For example, thepresent invention can be effectively applied, for example, to repair thepaints of ships and bridges.

Although the metal binder grinding tool segment forming the radiallyinner part of the tip constitutes the cutting-part main body 22 in theshown cutting part 20, the present invention is not limited thereto. Forexample, the cutting-part main body may be made of a different material(cemented carbide, etc.), and a hard sintered material forming theradially outer part of the tip and a grinding tool segment (grindingtool segments obtained by combining abrasive grains by a metal binder)forming the radially inner part of the tip may be secured side by sideto this cutting-part main body.

According to the present invention, a plurality of cutting parts may bearranged in two or more inner and outer rows (i.e. arranged on aplurality of concentric circles) on an opposed surface.

In the rotary tool according to the present invention, all the cuttingparts may not include the grinding tool segment 22 a and the hardsintered material tip 24 a as the cutting parts 20 do. First cuttingparts at least including a tip made of a hard sintered material andsecond cutting parts whose tip is entirely made of grinding tool segmentobtained by combining abrasive grains by a metal binder may be providedin a mixed manner on an opposed surface.

For example, as shown in FIGS. 6 and 7 as a second embodiment, cuttingparts (first cutting parts) 20 each including both the grinding toolsegment tip 22 a and the hard sintered material tip 24 a may beperipherally intermittently arranged, and cutting parts (second cuttingparts) 26 each including only a tip 26 a formed of the grinding toolsegment (grinding tool segment obtained by binding abrasive grains by ametal binder) may be arranged between adjacent cutting parts 20.Further, as shown in FIGS. 8 and 9 as a third embodiment, if acircumcircle C touching tips 26 a of cutting parts 26 is locatedinwardly of hard sintered material tips 24 a with respect to the radialdirections of the rotary segment 10, loads on the grinding tool segmenttips 22 a of the respective cutting parts 20 can be mitigated by therespective cutting parts 26.

Specifically, as shown in FIG. 10 as a fourth embodiment, even in such aconstruction that cutting parts each including only the hard sinteredmaterial tip 24 a are provided at positions radially more outward thanthe cutting parts 26 (cutting parts made by the hard sintered materials24 are secured in recesses 16 formed in the opposed surface of therotary segment 10 in the shown example), i.e. even in such aconstruction that the grinding tool segment tips 22 a shown in FIG. 1and other figures are deleted, the tips 26 a of the cutting parts 26 amade of the grinding tool segment can suppress excessive cutting-in,assist cutting by the tips 24 a and grind off or finish scratches causedby the cutting by the tips 24 a.

Further, as shown in FIG. 11 as a fifth embodiment, the rotary tool maybe such that a grinding tool segment 28 having a shape continuous alonga peripheral direction of the rotary segment 10 (ring shape in the shownexample) is provided, and cutting parts each including the hard sinteredmaterial tip 24 a are provided at positions more outward than thisgrinding tool segment 28 with respect to the radial directions of therotary segment 10. In this way, even if the grinding tool segment 28 hasno tip, it can assist the cutting by the hard sintered material tips 24a by its abrading action, and the abrasion thereby can grind off orfinish scratches formed by cutting by the hard sintered material tips 24a. Of course, an effect of preventing excessive cutting-in can also begiven.

However, if all the cutting parts are those according to the presentinvention and peripherally arranged at even intervals as in the firstembodiment, cutting ability can be made uniform along peripheraldirection, thereby obtaining advantages of realizing a smoother removingwork and a longer life for the tool.

1. A cutting part for use in a rotary tool including a rotary segmenthaving an opposed surface opposed to a work surface, comprising a tipfor scratching off a surface portion of the work surface when the rotarysegment is pressed against the work surface while being drivinglyrotated about an axis extending in a direction normal to the opposedsurface, wherein an inner part of the tip with respect to a radialdirection is made of a grinding tool segment obtained by bindingabrasive grains by a metal binder and an outer part of the tip withrespect to the radial direction is made of a sintered material harderthan the grinding tool segment.
 2. A cutting part according to claim 1,wherein the outer part of the tip with respect to the radial directionis made of a polycrystalline diamond sintered material orpolycrystalline cubic boron nitride sintered material.
 3. A cutting partaccording to claim 1, wherein the entire tip excluding the tip part madeof the sintered material is made of a grinding tool segment obtained bybinding abrasive grains by a metal binder.
 4. A cutting part accordingto claim 1, wherein the length of the tip made of the sintered materialis set within a range of 1% to 67% of the entire length of the tip.
 5. Arotary tool, comprising: a rotary segment having an opposed surfaceopposed to a work surface; and a plurality of cutting parts arranged onthe opposed surface and each having a tip for scratching off a surfaceportion of the work surface in a peripheral direction, the rotary toolscratching off the surface portion of the work surface by pressing therespective cutting parts against the work surface while the rotarysegment is drivingly rotated about an axis extending in a directionnormal to the opposed surface, wherein: the opposed surface is arrangedwith a grinding tool segment obtained by binding abrasive grains by ametal binder; each of the cutting parts includes a tip made of asintered material harder than the grinding tool segment; and the tipmade of the sintered material is provided at a position more outwardthan the grinding tool segment with respect to radial direction of therotary segment.
 6. A rotary tool according to claim 5, wherein somecutting parts include tips made of the grinding tool segment and theother cutting parts include tips made of the sintered material harderthan the grinding tool segment, and the respective cutting parts arearranged such that the tips made of the sintered material are located atpositions more outward than the tips made of the grinding tool segmentwith respect to the radial directions of the rotary segment.
 7. A rotarytool according to claim 5, wherein the grinding tool segment has such ashape continuous along a peripheral direction of the rotary segment, andthe cutting parts having the tips made of the sintered material areprovided at positions more outward than the grinding tool segment withrespect to the radial directions of the rotary segment.
 8. A rotarytool, comprising: a rotary segment having an opposed surface opposed toa work surface; and a plurality of cutting parts arranged on the opposedsurface and each having a tip for scratching off a surface portion ofthe work surface in a peripheral direction, the rotary tool scratchingoff the surface portion of the work surface by pressing the respectivecutting parts against the work surface while the rotary segment isdrivingly rotated about an axis extending in a direction normal to theopposed surface, the plurality of cutting parts including at least onecutting part having a tip whose inner part with respect to the radialdirection is made of a grinding tool segment obtained by bindingabrasive grains by a metal binder and whose outer part with respect tothe radial direction is made of a sintered material harder than thegrinding tool segment.
 9. (canceled)
 10. A rotary tool according toclaim 8, wherein the plurality of cutting parts include a first cuttingpart having a tip made of sintered material and a second cutting parthaving a tip made of grinding tool segment, the second cutting partbeing arranged such that the tip thereof is located at a position moreinward than the tip of the first cutting part made of sintered materialwith respect to the radial direction of the rotary segment.
 11. A rotarytool according to claim 8, wherein all the cutting parts of the rotarytool are cutting parts have a tip whose inner part with respect to theradial direction is made of a grinding tool segment obtained by bindingabrasive grains by a metal binder and whose outer part with respect tothe radial direction is made of a sintered material harder than thegrinding tool segment.
 12. A rotary tool according to claim 11, whereinthe outer part of the tip with respect to the radial direction is madeof a polycrystalline diamond sintered material or polycrystalline cubicboron nitride sintered material.
 13. A rotary tool according to claim11, wherein the entire tip excluding the tip part made of the sinteredmaterial is made of a grinding tool segment obtained by binding abrasivegrains by a metal binder.
 14. A rotary tool according to claim 11,wherein the length of the tip made of the sintered material is setwithin a range of 1% to 67% of the entire length of the tip.
 15. Arotary tool according to claim 11, wherein all the cutting parts havinga tip whose inner part with respect to the radial direction is made of agrinding tool segment obtained by binding abrasive grains areperipherally arranged at even intervals.
 16. A rotary tool according toclaim 8, wherein the outer part of the tip with respect to the radialdirection is made of a polycrystalline diamond sintered material orpolycrystalline cubic boron nitride sintered material.
 17. A rotary toolaccording to claim 8, wherein the entire tip excluding the tip part madeof the sintered material is made of a grinding tool segment obtained bybinding abrasive grains by a metal binder.
 18. A rotary tool accordingto claim 8, wherein the length of the tip made of the sintered materialis set within a range of 1% to 67% of the entire length of the tip.